Bacterial spores are among the most extraordinary cell types found in nature. These specialized dormant cells are resistant to virtually all forms of environmental assault but retain the capacity to metamorphose into a growing cell as soon as conditions are favorable. These abilities depend on the outermost protective shell that surrounds the spore, a multilayered protein armor called the coat, which gives the spore structural integrity and excludes all large molecules. In spite of the amazing capabilities bestowed on spores by the coat, we know relatively little about how it is built and how it provides protection. In this proposal, we seek to identify the contacts between known coat proteins in Bacillus subtilis spores as well as to discover novel coat proteins and the contacts they make within the coat. In particular, we will determine which coat proteins interact with two key proteins, called CotE and SpoIVA, that play important roles in coat assembly. These studies will help us understand the formation of this highly resistant cell type and the basis for its durability. Ultimately, we intend to define the biochemical interactions that direct spore coat assembly. This will provide a broader understanding of the molecular basis of complex assembly events, a question of general relevance to cell biology. The interest of this project is not confined to basic research, however, as bacterial spores from a variety of organisms, particularly clostridia, are major food pathogens and the spores produced by a relative of B. subtilis, B. anthracis, can be used as a highly effective bioweapon. Much of the potency of these pathogens is due to the coat, which permits rapid spore dispersal and makes decontamination very difficult with current technology. Studies of coat assembly may reveal novel approaches to combat these disease-causing agents.